e insulin receptor of Chinese hamster ovary (CHO) cells has been identified d characterized. Insulin growth factor-1 binding has also been evaluated. o mutant cell lines have been used to examine the role of glycosylation in ceptor function. The oligosaccharide portion of both receptor and/or n-receptor glycoproteins is involved in receptor binding and influences sulin receptor affinity but not IGF-1 receptor affinity. The biosynthesis d insertion into the plasma membrane of the insulin receptor occurs rmally even in two mutant cell lines with major defects in protein ycosylation. Lectins have been used as probes to confirm the glycosylation atus of the insuln receptor in these CHO lines. Insulin binding to the ucose starved cells resembles that of the mutant cell line demonstrating at it is indeed the glycosylation defect in these cells that leads to tered insulin binding. The other mutant cell line abnormally regulates its sulin receptor. The low affinity binding to this cell line mimics data tained with several human fibroblast cell lines cultured of severely sulin resistant patients. The effect of hydrocortisone on insulin ceptors of cultured human lymphocytes (IM-9) was studied using radiolabeled gars. In hydrocortisone-treated cells incorporation of radiolabeled sugars to the mature insulin receptor subunits was increased 2-3 times greater an in nontreated cells. The radioactivity incorporated into munoprecipitable receptor components was separated by polyacrylamide gel ectrophoresis. This model system can be used to study other agents that y act early in insulin receptor biosynthesis.